The present invention relates to improvements in an apparatus for automatic floor arrival at the time of service interruption in an A. C. elevator which is operated on the basis of an A. C. variable-voltage and variable-frequency control.
There have been proposed various apparatuses by which an elevator cage having stopped midway between floors at the time of service interruption is automatically caused to arrive at a floor. In this regard, it is common practice to use a D. C. power source (in general, a battery power source) having a small output current i.e., small capacity, thereby to enable an economical apparatus. To this end, it is common that a load in the cage is detected by any method, that the weight of the cage side and the weight of a counterweight side are compared, and that the elevator is operated in the direction of lowering the heavier of the two (hereinbelow, this direction shall be termed the "burden lowering direction", and the opposite the "burden raising direction").
In case of detecting the cage load by means of a weighing instrument, the detection accuracy is usually reduced due to various conditions such as the positions of passengers in the cage, the operating condition changes of the instrument and the mechanical factors of the instrument, whereby the elevator cannot always be operated in the burden lowering direction. Moreover, when an elevator which is already installed is remodeled so as to add the apparatus for automatic floor arrival at service interruption, the weighing instrument must be mounted. The mounting is very difficult, and a large cost is required for the remodeling.
Methods of operating an elevator in the burden lowering direction without providing any weighing instrument have been proposed in view of the above drawbacks, and an example thereof is disclosed in Japanese Patent Application Laid-open No. 54-3748. The prior-art apparatus for automatic floor arrival at service interruption in an A. C. elevator which uses a constant-voltage and constant-frequency control (CVCF) type inverter will be explained with reference to FIGS. 5 to 7. FIG. 5 is a block circuit diagram of the prior-art apparatus, FIG. 6 is a diagram of the relationships of the cage speed-the torque curve and the load torques at the time of a constant frequency (in the case where a start command has been issued in the burden raising direction), and FIG. 7 is a diagram of the relationships of the cage speed-the time with parameters being loads in a cage.
Referring to FIG. 5, the elevator system is constructed of an A. C. power source 1 which supplies electric power, a service interruption detecting relay 2 which detects the service interruption of the A. C. power source 1, a control device 3 which functions during the normal operation of the A. C. power source 1, an induction motor 4 which is operated on the basis of the control device 3, a speed detector 5 which detects the speed of a cage 8 in terms of the rotating speed of the induction motor 4, the cage being run by the rotation of the motor, a sheave 6 which is driven by the rotation of the induction motor 4, a rope 7 which is wound round the sheave 6, the cage 8 being attached to one end of the rope 7 and a counterweight 9 to the other end of the rope 7.
In the figures, the prior-art apparatus for automatic floor arrival at service interruption comprises a D. C. power source 10 which feeds electric power during the service interruption of the A. C. power source 1, starting contactors 11 which are made up of normally-open contacts adapted to close upon lapse of a predetermined period of time after the energization of the service interruption detecting relay 2, a constant-frequency inverter 12 which inverts the current of the D. C. power source 10 into alternating current, an operating direction change-over circuit 13 which determines and switches the operating direction of the elevator to either the burden lowering direction or the burden raising direction at the time of the service interruption, and a control circuit 14 for the service interruption state, which controls the operation during the service interruption on the basis of the detected result of the speed detector 5. It is constructed so as to automatically cause the cage of the elevator system to arrive at a floor at the time of the service interruption.
Next, the operation of the prior-art apparatus will be explained. During the normal operation of the elevator system, namely, when the A. C. power source 1 is in the conducting state, the service interruption detecting relay 2 is not energized, and the induction motor 4 is controlled by the control device 3 by using the A. C. power source 1 as a power supply, so that the cage 8 is run on the basis of the rotation of the induction motor 4.
Further, at the time of the service interruption of the A. C. power source 1, the service interruption detecting relay 2 is energized, and, upon the lapse of a predetermined period of time after the energization, the starting contactors 11 operate, whereby the operating direction change-over circuit 13 provides a command of the operation in a predetermined direction (herein, assumed to be the ascending direction). Consequently, current fed by the D. C. power source 10 is inverted into a three-phase alternating current by the constant-frequency inverter 12, and the three-phase alternating current is applied to the induction motor 4, so that the cage 8 moves in the ascending direction on the basis of the command of the operating direction change-over circuit 13.
The torque characteristics of the prior-art apparatus will be explained with reference to FIG. 6. Assuming now that the cage 8 having no load therein be run in the descending direction, the load torque on this occasion as viewed from the induction motor 4 becomes a no-load state load torque T.sub.N having a minus value. Therefore, an acceleration torque T.sub.AN at the time of start can be expressed as (a starting torque T.sub.S)-(the no-load state load torque T.sub.N). Similarly, an acceleration torque T.sub.AB in a balanced state can be expressed as (the starting torque T.sub.S)-(a balanced state load torque T.sub.B). In addition, an acceleration torque T.sub.AH in the case where the load in the cage 8 is somewhat heavier than the counterweight 9 (for example, a 70% load) can be expressed as (the starting torque T.sub.S)-(a load &gt; counterweight state load torque T.sub.H). Further, an acceleration torque T.sub.AF in a rated load state can be expressed as (the starting torque T.sub.S)-(a rated load state load torque T.sub.F). When the respective acceleration torques mentioned above are compared, the following holds: EQU T.sub.AN (=T.sub.S -T.sub.N)&gt;T.sub.AB (=T.sub.S -T.sub.B)&gt;T.sub.AH (=T.sub.S -T.sub.H)&gt;T.sub.AF (=T.sub.S -T.sub.F)
Accordingly, as the load torque viewed from the induction motor 4 is greater with respect to a speed command V.sub.C, the period of time in which a predetermined speed V.sub.S is reached needs to be longer (illustrated in FIG. 7).
In FIG. 7, V.sub.NL indicates a no-load state acceleration curve, V.sub.BL a balanced state acceleration curve, V.sub.HL a (load &gt; counterweight) state acceleration curve, and V.sub.FL a rated load state acceleration curve. Periods of time T.sub.1, T.sub.2 and T.sub.3 indicate the periods of time in which the curves V.sub.NL, V.sub.BL and V.sub.HL reach the predetermined speed V.sub.S, respectively.
The speed detector 5 detects the moving speed of the cage 8 (the cage speed) by utilizing the above characteristics, and delivers it to the service interruption state control circuit 14 as a speed signal. In a case where the moving speed of the cage 8 has reached the predetermined speed V.sub.S in the predetermined period of time after the start (corresponding to the period of time T.sub.2 indicated in FIG. 7), the speed detector decides a light load for the induction motor 4 (namely, burden lowering), so that the operation in the burden lowering direction is continued until the cage arrives at the nearest floor.
In contrast, in a case where the moving speed of the cage 8 does not reach the predetermined speed V.sub.S upon lapse of the predetermined period of time (T.sub.2) after the start, the speed detector decides a heavy load for the induction motor 4 (namely, burden raising), so that the operating direction of the initial start command (the ascending direction in this case) is switched to operate the elevator in the burden lowering direction.
As thus far stated, in the prior-art system which uses the constant-voltage and constant-frequency (CVCF) type inverter, the operation has been a very effective expedient.
In recent years, the progress of control technology with power semiconductors has been remarkable, and there has been developed an A. C. elevator in which a slip frequency control is performed using a variable-voltage and variable-frequency control type inverter, in order to efficiently operate the elevator even at the time of service interruption and to attain a more comfortable ride and enhance a floor arrival precision.
The A. C. elevator which is subjected to the slip frequency control will be explained with reference to FIGS. 8 to 10. FIG. 8 shows a general circuit block diagram of the slip frequency control, FIG. 9 an equivalent circuit diagram of an induction motor, and FIG. 10 a diagram of the relationships between the running speed of a cage and time.
Referring to FIG. 8, the A. C. elevator which is subjected to the slip frequency control has the rotation of an induction motor 4 controlled by a slip frequency control circuit 20. The slip frequency control circuit 20 is constructed of a speed command circuit 21 which produces a speed command .omega..sub.p in accordance with an external input, an adder 22 which receives the speed command .omega..sub.p and a cage speed .omega..sub.r from a speed detector 5 to compare and operate them, a speed control amplifier 23 to which the operated result of the adder 22 is applied and which delivers a torque current command T.sub.C, a current amplitude command circuit 24 which determines and commands the value of a primary current I.sub.1 on the basis of the torque current command T.sub.C, a slip frequency calculator 25 which produces a slip frequency command .omega..sub.s on the basis of the torque current command T.sub.C, an adder 26 which receives the slip frequency command .omega..sub.s and the cage speed .omega..sub.r of the speed detector 5 to compare and operate them, thereby to deliver a frequency command .omega..sub.1, a current command generator circuit 27 which, on the basis of the values of the frequency command .omega..sub.1 and the primary current I.sub.1, produces respective current commands i.sub.u ', i.sub.v ' and i.sub.w ' for determining the values of a three-phase alternating current, current control amplifiers 28 to which the current commands i.sub.u ', i.sub.v ' and i.sub.w ' and feedback current values (motor current values) i.sub.u, i.sub.v and i.sub.w detected by current detectors 31h, 31h and 31h are respectively applied so as to control primary currents, and a power converter 29 which supplies the induction motor 4 with electric power on the basis of the outputs of the current control amplifiers 28.
Next, the operation of the slip frequency control circuit 20 will be explained in conjunction with FIG. 9 showing an equivalent circuit of the induction motor 4. In the figure, V.sub.1 indicates a primary voltage, R.sub.1 a primary winding resistance, l.sub.1 a primary side reactance, I.sub.1 a primary side current, R.sub.2 a secondary winding resistance, l.sub.2 a secondary side reactance, I.sub.2 a secondary side current, L a copper loss, I.sub.M an exciting current, E.sub.1 a primary induced voltage, and (1-S/S)R.sub.2 a load resistance.
As to the equivalent circuit shown in FIG. 9, a machine output P.sub.M is expressed by the following equation: ##EQU1## Accordingly, an output torque T.sub.M becomes: ##EQU2## where .omega..sub.O : input angular frequency of the motor, S: slip,
.omega..sub.s : slip angular frequency.
Meanwhile, assuming .omega..sub.O l.sub.2 &lt;&lt;R.sub.2 /S, the following holds: ##EQU3## When Eq. (4) is substituted into Eq. (2), the following holds: ##EQU4## As apparent from this equation (5), when E.sub.1 /.omega..sub.O (corresponding to the gap flux of the motor) is controlled to be constant, the torque T.sub.M is proportional to the slip angular frequency (slip angular speed) .omega..sub.s.
Thus, as understood from the foregoing circuit arrangement in FIG. 8 with the A. C. elevator which is operated under the slip frequency control, when the load torque of the induction motor 4 is great, the slip frequency command .omega..sub.s increases, and the current commands i.sub.u ', i.sub.v ' and i.sub.w ' to be delivered from the current command generator circuit 27 increase, so that the feed power to the induction motor 4 increases. Therefore, the property of following up the speed command of a rescue operation at the time of service interruption becomes very good irrespective of the magnitude of the load torque of the induction motor 4. Such relations are shown in FIG. 10.
More specifically, with the A. C. elevator which is operated under the slip frequency control, when the rescue operation is performed at the service interruption, some speed difference arises in the acceleration mode, but both the burden raising and burden lowering operations follow up the speed control without any considerable difference and therefore a difference in cage speeds does not develop depending upon the magnitude of the load torque. Disadvantageously, this makes it very difficult in that, as in the preceding example, the load in the cage is detected on the basis of whether or not the cage speed reaches the predetermined value after the predetermined period of time since the start, whereupon the elevator is operated in the burden lowering direction.